"As for "floor truss" systems, yes those have merit in some areas and application...though not typical for most domestic timber frame needs/requirements of load..."
Since I have a 'round' floorplan, and at present do not intend on having strategically-placed lower walls (just two columns near the center) I thought it might be desirous for strength reasons --granted I still need to run the numbers, but the 15-20ft span seemed a bit large unless giant joists are used, if I am to have a rigid floor surface. It is interesting that dual floors/truss floors aren't more common, though, since they do much of the same types of jobs as a roof.

TCB